The present invention relates to a gas furnace, and more particularly to a gas furnace with a heat exchanger that forms serpentine combustion gas flow paths.
Some gas furnaces include a plurality of heat exchangers spaced apart to allow airflow between them. A pair of plates, disposed in face-to-face relation and secured together, form each heat exchanger. The plates define flow paths for hot combustion gases provided by the furnace burners. Heat transfers through the plate portions which define the flow paths to the air flowing around the heat exchangers. The heated air then flows to the area requiring heating.
Such gas furnaces should meet the following requirements:
a. The temperature of combustion gases that discharge from the exchanger must be sufficiently high to avoid the formation of condensation in the heat exchanger during operation; PA1 b. The temperature shear or temperature differential in the heat exchanger must be gradual and consistent from the exchanger's combustion zone to its exhaust zone; thus, minimizing thermal stress in the walls of the heat exchanger; PA1 c. Hot combustion gases must not stratify, and they must accelerate as they move through the exchanger to enhance internal gas-to-surface heat transfer; PA1 d. The passageways defining the flow paths for the combustion gases in the heat exchanger must maintain a constant dynamic pressure distribution for the gases; PA1 e. The exterior surface to air turbulence for the heat exchanger must be sufficiently high to maximize heat transfer per vertical inch of height; PA1 f. The furnace must have a compact construction that minimizes the expense of manufacture, assembly and transport.
The prior art includes a wide variety of the gas furnaces described above; however, because of various inherent design characteristics, the prior furnaces do not fulfill the above-noted criteria. For example, the prior art includes heat exchangers made from formed tubing. Those heat exchangers tend to be efficient and compact, but they are expensive to manufacture and require sophisticated tube forming and joining equipment. The prior art also includes serpentine clamshell heat exchangers, which are less expensive and easier to manufacture than the tube heat exchangers, but tend to be less efficient and larger in size. In contrast, the furnace of the present invention meets the above criteria and provides a compact construction that maximizes heat transfer. It provides the low cost and ease of manufacture of the clamshell heat exchangers and the high efficiency and compact size of the tube heat exchangers.